At the very beginning of my hairdresser career, I used ol' good Google Calendar to record both personal and work appointments.
Since then I've tried lots of different apps, but for me most of them either expensive or complex with lots of functions I'd never use.
The thing is if you have a few hours per day to manage all your bookings and have other activities to deal with - Google, diary or similar apps will suit you better than some special booking or time-management apps.
At the moment I use Tap2Visit app, it's free and serves my needs, but the online booking is tricky - the clients can book only through the app, may appear not convenient.